Final answer:
Intrasexual selection in males leads to traits that enhance competition with other males, such as size and strength. Intersexual selection results in traits that make males more attractive to females, even if these traits reduce survival chances. Both types of selection contribute to sexual dimorphism in species.
Step-by-step explanation:
In the process of sexual reproduction, certain selection pressures lead to the development of specific traits in males through intersexual and intrasexual selection. Intrasexual selection generally results in traits that enhance a male's ability to compete with other males for mating opportunities. Examples of these traits include greater size, strength, aggression, and the ability to engage in combat, like rams butting heads. These traits often require considerable energy but are indicators of health and dominance.
Conversely, intersexual selection, where individuals of one sex choose mates of the other sex, often leads to traits that may not enhance survival but increase attractiveness to potential mates. Male peacocks with bright plumage and birds that perform elaborate mating dances are examples of traits favored by intersexual selection. These traits may even be detrimental to survival, as they can attract predators or hinder escape, illustrating the handicap principle.
Overall, intrasexual selection tends to favor traits that emphasize physical prowess, while intersexual selection favors traits that improve mate attractiveness, leading to a wide variety of secondary sexual characteristics and pronounced sexual dimorphism in some species.